The present disclosure relates to conveyor systems and particularly to conveyor systems having a strapping station at which a load is wound with more than one strap to hold the load together.
Conveyors play a central role in the packaging and transport of sheet products, such as corrugated sheet material. Conveyors carry a newly manufactured sheet to various stations where stacks of sheets are formed and eventually loaded onto pallets for shipment. In some cases, where the sheets are smaller in size, multiple stacks of sheets may be loaded onto a single pallet. Once the sheets have been loaded onto a pallet it is typically necessary to constrain the stacks to retain them on the pallet. Strapping machines are used to automatically wind one or more straps around a palletized load. In most cases, multiple straps are used with the straps spaced uniformly across the length of the load or each stack in a load. The straps are guided through the pallet beams and around the upper surface of the load where they are automatically cinched and clamped in a conventional manner.
In the strapping operation it is important to squeeze or compress the load as the strap is affixed around the load. Prior art systems drop a platen onto the upper surface of the load, applying the strap while the platen remains on the load. The platen is then lifted and the load is advanced to another location, at which point another strap is applied in the same manner. This process may be repeated two or more times for a given load. One problem that arises is that when the platen is lifted the compression of the load is relieved. Thus, on a load that requires multiple straps, the load will be under an uneven force from the strap during the period when the compression is relieved. This uneven loading can cause damage to the load, particularly on the top sheet. In addition, the first strap applied must be strong enough to hold the entire load under compression while the load is situated to receive additional straps. This requires the straps to be stronger than necessary to constrain the load, requiring more material for the straps than is needed.
Furthermore, although the load is squeezed again when the platen is dropped for the next strap, the amount of compression is rarely the same. This leads to multiple straps applying varying degrees of compression on the load. In a worst case scenario, greater compression at one strap may lead to loosening and dislodgment of an adjacent strap. Nominally though, the inconsistent compression leads to an uneven load surface which can create problems if loads are stacked or may compromise the quality of the stacked sheets.